Food on the brain
When is a calorie in effect more than a calorie? When it is part of products that are hyper-palatable – maybe even advertised and promoted as habit-forming
Our news team reports. Some food may well be addictive, in all the usual senses of the word. New research results (1) indicate that diets heavy in saturated fats and added sugars, of the type that cause overweight and obesity, may cause changes in the brain, which drive more and more overeating of those foods. If so, this is a powerful explanation of why obese people almost always rebound to their previous level of body fat after going on a dieting regime.
This study was however of rodents. Moreover, the study showed that overconsumption of fatty diets by the rats damaged or at least altered their blood-brain barrier. 'Substances that are not supposed to get to the brain are getting to it because of this breakdown' says lead author Terry Davidson. 'You start throwing things into the brain that don't belong there, and it makes sense that brain function would be affected.'
On unsuccessful attempts to shed excess fat, he says 'I do think it [the damage] becomes permanent… Other research has found that obese people and formerly obese people have weaker hippocampal activity when consuming food than do people who have never been obese. Just because you lose the weight doesn't mean you regain the brain function. This could help explain why it is so difficult for formerly obese people to keep the weight off.'
Is this a speculation too far? Can findings of studies of rodents apply to humans? In this case the answer looks like being yes. A study of children published last month (2) has come to similar conclusions. When compared with normal-weight brothers and sisters, overweight and obese 5-12 year-old children ate 34 percent more calories from snack foods even after eating a meal. Even after eating a full meal, overweight and obese children were liable to continue to snack than their normal weight brothers and sisters.
Lead author Tania Kral says: 'The overweight and obese siblings showed an impaired ability to adjust for calorie differences and consumed more snacks even when satiated. These findings suggest some children are less responsive to their internal cues of hunger and fullness and will continue eating even when full.'
These findings and provisional conclusions are startling. But the idea that some food products are addictive is not brand-new. Box 1 summaries results of another study done at Yale University whose authors include Kelly Brownell. A further study (4) of hyper-palatable food products linked here, also comes to much the same conclusion. What remains to be determined, is exactly what types of product are most likely to cause compulsive over-consumption. It may well be that these include products deliberately formulated to be habit-forming.
Drug and food addiction, what's the difference?
Time Magazine published this story by Maia Szalavitz earlier this year. This is a shortened version. Is Häagen-Dazs ice cream as addictive as heroin? Or, put another way, is heroin as addictive as Häagen-Dazs? Depending on how you phrase the question, you're either asking whether heroin addiction is no more serious than a love of junk food, or you're questioning whether junk food junkies may have a serious disorder that needs intervention. A new study suggests that there may be no clear, bright line between addictive and normal responses—and adds to the evidence that all 'addictions' act on the same motivational system in the brain.
The study, published in the Archives of General Psychiatry (3) involved 39 healthy women, who ranged in weight from lean to overweight or obese. The participants were asked to complete the Yale Food Addiction Scale, which tests for signs of food addiction. Women with full-fledged eating disorders of any type were not included in the study.
Then, using fMRI, researchers led by Yale's Ashley Gearhardt and Kelly Brownell looked at the women's brain activity in response to food. In one task, the women were asked to look at pictures of either a luscious chocolate shake or a bland, no-calorie solution. For another brain-scan task, women actually drank the shake — made with four scoops of vanilla Häagen-Dazs ice cream, 2% milk and 2 tablespoons of Hershey's chocolate syrup — or the no-calorie control solution, which was designed to be as flavourless as possible (water couldn't be used because it actually activates taste receptors).
The scientists found that when viewing images of ice cream, the women who had three or more symptoms of food addiction — things like frequently worrying about overeating, eating to the point of feeling sick and difficulty functioning due to attempts to control overeating or overeating itself — showed more brain activity in regions involved with pleasure and craving than women who had one or no such symptoms.
These areas included the amygdala, anterior cingulate cortex and medial orbitofrontal cortex — the same regions that light up in drug addicts who are shown images of drug paraphernalia or drugs. Similar to people suffering from substance abuse, the food-addicted participants also showed reduced activity in brain regions involved with self-control (the lateral orbitofrontal cortex), when they actually ate the ice cream.
In other words, women with symptoms of food addiction had higher expectations that a chocolate shake would be yummy and pleasurable when they anticipated eating it, and they were less able to stop eating it once they started. Interestingly, however, unlike drug addicts, the participants with more signs of food addiction did not show a decrease in activity in pleasure-related regions of the brain when they actually ate the ice cream. People with drug addictions tend to derive less and less pleasure from drug use over time — they want drugs more but enjoy them less, creating compulsive behavior. But it's possible that this tolerance may be seen only in serious addictions.
- Davidson T, Monnot A, Neal A, Martin A, Horton J, Zheng W. The effects of a high-energy diet on hippocampal-dependant discrimination performance and blood-brain barrier integrity differ for diet-induced obese and diet- resistant rats. Physiology &Behavior, 2012; 107 (1): 26 DOI: 10.1016/j.physbeh. 2012.05.015
- Kral, T, Allison D, Birch L, Stallings V, Moore R, Faith M.. Caloric compensation and eating in the absence of hunger in 5- to 12-y-old weight- discordant siblings. American Journal of Clinical Nutrition, 2012; 96, 3,: 574-583 DOI: 10.3945/ajcn.112.037952
- Gearhardt A, Yokum S, Orr P, Stice E, Corbin W, Brownell K. Neural correlates of food addiction. Archives of Psychiatry 2011, 68, 8. http://archpsyc.jamanetwork.com/article.aspx?articleid=1107239
- Gearhardt A, Grillo C, DiLeone R, Brownell K, Potenza M. Can food be addictive? Public health and policy implications. Addiction 2011, 106, 1208- 1212.